Schottky Mass Measurements of Cooled Proton-Rich Nuclei at the GSI Experimental Storage Ring

High-precision mass measurements of proton-rich isotopes in the range of $60\le Z\le 84$ were performed using the novel technique of Schottky spectrometry. Projectile fragments produced by ${}^{209}$Bi ions at 930A MeV were separated with the magnetic spectrometer FRS and stored and cooled in the experimental storage ring (ESR). A typical mass resolving power of 350 000 and a precision of 100 keV were achieved in the region $A\approx 200$. Masses of members of $\alpha$ chains linked by precise $Q_{\alpha }$ values but not yet connected to the known masses were determined. In this way it is concluded that ${}^{201}$Fr and ${}^{197}$At are proton unbound.